Heavy dye loads on bond paper of various colored inks can lead to bleed and reduction of waterfastness. Bleed, as used herein, is the invasion of one color into another color on paper, which is a surface phenomenon. This is in contradistinction to uses of the term in the prior art, which tend to define "bleed" in the context of ink of a single color following the fibers of the paper; this is a sub-surface phenomenon.
Surfactants have been used as anti-clogging agents in Japanese Laid-Open Patent Application No. 63-165465 for use in ink-jet recording inks. The surfactants used in that application are limited to those having a surface tension between 20 and 50 dyne/cm. The amount of surfactant ranges from about 0.5 to 25 wt %. Specific examples disclosed include sodium dodecyl benzene sulfonate, sodium laurate, and polyethylene glycol monooleyl ether.
Japanese Laid-Open Patent Application No. 01-203,483 is directed to ink-jet recording compositions. Bleed reduction is mentioned in connection with printing using the inks. However, the compositions require pectin (0.01 to 2 wt %), which is probably being used as a thickener. However, pectin is not useful in inks used in thermal ink-jet printers, due to its thermal instability (it gels at higher temperatures).
Japanese Patent JO 1215-875-A is directed to inks suitable for ink-jet printing, evidencing good recording with fast drying without bleeding. The compositions all require triglycerides. Such compounds, however, are not stable to extended shelf life necessary for commercial inks.
Japanese Patent JO 1230-685-A is directed to inks suitable for ink-jet printing, evidencing quick absorption on the surface of conventional office paper without smear or blotting. The compositions comprise colorants and liquid solvents and/or dispersants and are characterized by the presence of a copolymer of ethylene oxide and propylene oxide of the formula HO(C.sub.2 H.sub.4 O).sub.a -C.sub.3 H.sub.6 O(C.sub.2 H.sub.4 O).sub.b H, where a+b is up to 50 and b is optionally 0. These copolymers are referred to as "PLURONICS". For the most part, they have not been found to stop bleed.
Thermal ink-jet printers offer a low cost, high quality, and comparatively noise-free option to other types of printers commonly used with computers. Such printers employ a resistor element in a chamber provided with an egress for ink to enter from a plenum. The plenum is connected to a reservoir for storing the ink. A plurality of such resistor elements are arranged in a particular pattern, called a primitive, in a printhead. Each resistor element is associated with a nozzle in a nozzle plate, through which ink is expelled toward a print medium. The entire assembly of printhead and reservoir comprise an ink-jet pen.
In operation, each resistor element is connected via a conductive trace to microprocessor, where current-carrying signals cause one or more selected elements to heat up. The heating creates a bubble of ink in the chamber, which is expelled through the nozzle toward the print medium. In this way, firing of a plurality of such resistor elements in a particular order in a given primitive forms alphanumeric characters, performs area-fill, and provides other print capabilities on the medium.
Many inks that are described for use in ink-jet printing are usually associated with non-thermal ink-jet printing. An example of such non-thermal ink-jet printing is piezoelectric ink-jet printing, which employs a piezoelectric element to expel droplets of ink to the medium. Inks suitably employed in such non-thermal applications often cannot be used in thermal ink-jet printing, due to the effect of heating on the ink composition.
A need remains for ink compositions for use in ink-jet printing, particularly thermal ink-jet printing, which do not evidence bleed, as defined herein, and yet which possess relatively long shelf life and other desirable properties of such inks.